1. Field of the Invention
The present invention relates to a steering apparatus for a car with the enhanced retaining force of a telescopically adjustable steering column to a car body, and a method of manufacturing the same steering apparatus.
2. Related Background Art
Conventionally, it is required for a steering apparatus for a car to enhance the pressing force or the retaining force of a telescopically adjustable or tilt adjustable steering column to a car body.
For instance, Japanese Patent Application Laid-Open No. 10-35511 discloses a tilt/telescopic steering apparatus in which a steering column is arranged to be capable of being tilt adjustable and telescopically slidable and a fixed member to steering column is brought into pressure contact with a fixing member to car body to be fastened and retained by the use of a clamp mechanism at the time of tilt/telescopic clamp. Especially, at the time of clamp by the use of the clamp mechanism, a large number of thin friction plates made of metal are interposed between a fixing member to car body and the clamp mechanism so as to drastically enhance the retaining force (the pressing force) of the steering column to the car body.
Generally, the fixed member to steering column (e.g., a distance bracket) is formed with an elongated hole for telescopic adjustment through which a fastening bolt of a clamp member is inserted so as to guide the steering column in the axial direction. This fixed member to steering column is formed separately from the steering column and is secured to the steering column by welding or caulking when it is manufactured.
However, in the conventional steering apparatus for a car described above, since the fixed member to steering column (distance bracket) is separately formed from the steering column and welding or caulking is employed for its manufacture, the steering column itself can not be maintained to be of high rigidity. There is another problem that the manufacturing cost required for the materials, the processing works, assembly, etc., is increased and the total weight of the steering column is also increased.
Note that in the above-mentioned Japanese Patent Application Laid-Open No. 10-35511, in Japanese Utility Model Application Laid-Open No. 6-74562, and in EP0770537A1, a pair of flanges which are cut up from the steering column to be bent are provided with a pair of elongated holes for telescopic adjustment, and these elongated holes are formed on the steering column.
However, since the flanges are cut-up flanges, the steering column is formed to have an “open section”. Thus, the steering column itself can not be formed as having high rigidity, so that the high retaining force of the steering column to the car body can not be always maintained.
In Japanese Patent Application Laid-Open No. 8-276852 and in EP0721875A1, a swelled portion is formed as a unitary structure with a steering column by press work and this swelled portion is formed with a circular hole for tilt adjustment. Since the steering column has a “closed section” with this arrangement, the steering column itself can be maintained to have high rigidity. Moreover, this circular hole for tilt adjustment is a simple circular hole and is not extended in the axial direction, so that the swelled portion is small in size and can be easily formed by press work. However, when an elongated hole for telescopic adjustment which is largely extended in the axial direction is to be formed in the swelled portion, the swelled portion has to be formed to be elongated in the axial direction as a unitary structure with the steering column, so that it will be extremely difficult to realize such a structure if using the press work like that disclosed in the above disclosures.